Surges/Transients; Grounding - Emerson Rosemount Reference Manual

Reference Manual
00809-0100-4021, Rev GC
Figure 2-14. Load Limits
F
OUNDATION
Powered over F
operates between 9.0 and 32.0 Vdc, 11 mA maximum. Transmitter power terminals are rated to
42.4 Vdc.
The power terminals on the 3144P with F
2.6.1

Surges/transients

The transmitter will withstand electrical transients of the energy level usually encountered in
static discharges or induced switching; however, high-voltage transients, such as those induced
in wiring from nearby lightning strikes, can damage both the transmitter and the sensor.
The integral transient protection terminal block (option code T1) protects against high-voltage
transients. The integral transient protection terminal block is available as an ordered option, or
as an accessory. Refer to
information.
2.6.2

Grounding

Sensor shielding
The currents in the leads induced by electromagnetic interference can be reduced by shielding.
Shielding carries the current to ground and away from the leads and electronics. If the ends of
the shields are adequately grounded, only a small amount of current will actually enter the
transmitter.
If the ends of the shield are left ungrounded, voltage is created between the shield and the
transmitter housing and also between the shield and earth at the element end. The transmitter
may not be able to compensate for this voltage, causing it to lose communication and/or go into
alarm. Instead of the shield carrying the currents away from the transmitter, the currents will
now flow through the sensor leads into the transmitter circuitry where it will interfere with the
circuit operation.
Installation
Maximum Load = 40.8 X (Supply Voltage - 12.0)
4–20 mA dc
1240
1100
1000
750
500
250
0
10 20
12.0
Supply Voltage (Vdc)
fieldbus
fieldbus with standard fieldbus power supplies, the transmitter
OUNDATION
"Transient protection (option code T1)" on page 198
Operating
Region
30 40 42.4
fieldbus are polarity insensitive.
OUNDATION
Section 2: Installation
April 2014
for more
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